It is well known in the art of turf maintenance to use a grass cutting vehicle having the ability to turn within itself, commonly referred to as a zero turning radius (ZTR) lawn mower. A ZTR mower, such as a Ferris Model IS 500Z, is generally propelled by independently controlled rear drive wheels, which can be driven at variable radial velocities and directions. The disclosed system is an improvement to ZTR vehicles to allow them to safely traverse slopes. The system applies to any vehicle that utilizes a pair of independently driven wheels to accomplish both the forward and reverse motion as well as the steering along with a front or rear wheel(s) mounted as casters. This type of vehicle is commonly used for commercial and home mowers because of the vehicle's ability to turn quickly, make a turn with zero radius—pivoting on a point along the rear axle, and to reverse direction instantly. All of this saves time in mowing. The following disclosure will focus on four wheel mowers with two front casters and two independently driven rear wheels, but the disclosure should not be construed to apply only to mowers or only to vehicles with two front casters.
Steering of the ZTR is accomplished by driving each one of the independent drive wheels at different rates of speed with respect to the other. In doing so, the driven wheels force the mower to change its direction either to the left or right, thereby providing steering capabilities without any direct control linkage to the forward wheels. Hence, conventional caster wheels are advantageous in that they are responsive to the differential speed of the driven rear wheels and simply provide support for the frame and/or mower deck of the mower. In doing so the mower can be maneuvered in such a way so as to have a center of the turning radius located midway between the driven wheels, therefore a ZTR mower is able to turn about itself.
When traversing a slope, ZTR mowers must use the rear wheels to counteract the tendency of the mower to go down the slope due to gravity. This tendency is called “crabbing” because the mower cannot go straight across the slope, but goes at an angle as the operator continuously corrects the mower's path. When the slope is moderately steep or the traction that the rear wheels can achieve is low (such as in wet conditions or when the turf is soft), the rear wheels will often slide or tear up the turf and the mower will go down the hill regardless of how much steering input the operator uses.
Various mechanical systems have been proposed in order to try to correct this problem. U.S. Pat. No. 4,504,074 to Smith; U.S. Pat. No. 6,962,219 to Hauser, and U.S. Pat. No. 7,686,107 to Bland et al., all address the problem of the rear wheels sliding and the mower going downhill by adding a mechanical steering system to the front wheels. These solutions miss the point. They interfere with the utility of a ZTR mower because they prevent instant changes in direction and prevent instant reversing of the mower. There is no point to having a ZTR mower if it has a steering wheel that has to be rotated to change direction.
ZTR mowers tend to “steer” themselves down hill because the front wheels are mounted as casters well in advance of the rear drive wheels and naturally rotate about their vertical axis as gravity applies a side force to the mower when on a slope. The system disclosed herein counteracts the rotational force that gravity induces in the casters. Thus, just like on flat ground, the casters have a neutral turning force on them; they are in balance. Therefore, the operator can turn uphill or downhill, stop, reverse or make any other maneuver without the rear wheels having to do the extra work of overcoming the side force generated by gravity on the front of the mower. By eliminating this extra work that the rear wheels have to do, sliding and tearing of the turf is eliminated. The disclosed system does not interfere with the natural operation of the ZTR mower, and is “transparent” to the operator, yet allows the mower to operate even on steep slopes as if it were on flat ground. The system also includes a safety feature to help prevent rollovers (something the mechanical systems do not do).
The disclosed system includes, in combination, an electronic subsystem to measure the angle of the mower (side-to-side) and calculate a balancing force necessary to neutralize the effects of gravity on the front of the mower, and a pneumatic subsystem, receiving the output of the electronic subsystem, to deliver a rotational force to the caster(s) without interfering with the ability of the caster(s) to rotate freely.
The electrical subsystem uses a device for measuring the proper acceleration of the vehicle from side to side (i.e., in a direction perpendicular to the front-to-rear axis of the mower). Proper acceleration is the acceleration an object experiences relative to freefall as opposed to relative to a coordinate system. Such a device is generally referred to as an accelerometer or inclinometer (or clinometer), and produces an output that characterizes the angle that the device senses. The accelerometer is located just in front of the rear wheel axles, where it will not be affected by forces produced when the mower is turned sharply. In addition, smoothing of the accelerometer output is provided to minimize the effects of vibration and rough terrain. The electronic system can be analog or digital. In one embodiment, an analog system is disclosed, in an alternative embodiment a digital system is disclosed, which may be preferable as it eliminates the manual tuning that an analog system requires. Nonetheless, the analog embodiment disclosed is representative of a prototype made with an analog controller.
The electrical subsystem carries out a plurality of functions in addition to producing a signal representative of the angle of the mower. First, the electrical subsystem is set to produce an output appropriate for the particular type of mower on which the system is installed. Each type of mower has a different amount of weight on the front caster wheels, and this weight determines the rotational force that gravity induces in the casters. The electrical subsystem is programmed or “tuned” to produce the correct output for any given angle that the mower could be at. Second, in one embodiment the electrical subsystem uses a cam and switch system to cut off the pneumatic control (e.g., air pressure) to a caster when it is rotated more than about 60 degrees away from the caster position when the mower is moving straight forward. This means there is no rotational force or bias applied from the pneumatic system when the casters are sharply rotated, such as when the mower is going backwards or making an extremely sharp turn. As will be described in more detail below, each caster has its own cam/switch control system such that both casters' pneumatic systems will not be turned off if one caster is rotated extremely while the other is not. Third, the electrical subsystem recognizes when the mower is at the maximum angle at which it can be operated safely. A regular ZTR would not usually be able to approach its maximum safe angle of operating because the rear wheels would lose traction before it got near to its rollover point. With systems that improve the ability of the mower to traverse steep slopes, the operator could theoretically take the mower to an unsafe angle of operation, just like he could with a normal tractor type mower. The electrical subsystem is programmed to prevent the operator from approaching the rollover angle. This can be done in several ways. The simplest way is for the system to turn itself off. This results in the casters being allowed to then rotate under the force of gravity, and the mower simply turns down the hill because the casters are no longer biased to enable the mower to hold the steep angle across the face of the slope. The system can turn on an alarm and/or force the drive wheel speed control levers to a neutral position (this requires additions to the pneumatic system or other components of the mower).
In response to the electrical subsystem, the pneumatic subsystem provides the balancing torque to the casters while still allowing them to rotate freely. The pneumatic subsystem consists of a small air compressor, an air reservoir, a pressure switch to control the air compressor, an electro-pneumatic pressure regulator, two double acting air cylinders (one for each caster), a small air reservoir, and an air valve for each port of each air cylinder (e.g., four valves for a normal mower with two front casters each having its own pneumatic cylinder). The electrical subsystem output controls the electro-pneumatic pressure regulator and the air valves based on the angle of the mower. A lever arm is attached to the rotating spindle of each caster (as described in more detail below), and an air cylinder is attached to each lever arm with a rotatable joint so that each caster can rotate freely 360-degrees without interference from the air cylinder. The opposite end of each cylinder is fixed to the frame of the mower or to the front suspension crossbeam if the casters are mounted on a suspended or pivotable axle. When the mower is operated at an angle, the electrical subsystem produces a signal that is output to the electro-pneumatic pressure regulator to produce the correct pressure to balance the torque being induced by gravity on the casters. The weight of the front end of the mower, the length of the lever arm, the diameter of the air cylinders, and the offset of the casters are all factors that impact this pressure. The proper air valves are turned on so that each caster receives a correct balancing or biasing force. The electro-pneumatic pressure regulator is connected both to the air valves and to a small air reservoir having two to three times the volume of the air cylinders on the machine. As the mower traverses a slope, the operator may turn the mower to go around obstacles or follow contours. When this occurs, the casters will naturally change angle, thus changing the volume of air in the air cylinders. The small reservoir is intended to absorb the changes without the electro-pneumatic pressure regulator having to supply more air or vent excess air. This conserves compressed air and makes the system instantly responsive and much more transparent to the operator.
An object of the disclosed embodiments is to provide a neutralizing or balancing force on at least one caster to offset the rotational force induced by gravity when driving the mower across a slope.
It is a further object to ensure that balancing force is transparent to the operator during normal operation of the mower.
It is yet another object of the disclosed embodiments to prevent the accidental rolling over of a mower when cutting on a severe slope by an action including (a) allowing the ZTR mower to naturally turn downhill; (b) provide a warning alarm; and/or (c) reduce the speed or drive power applied to at least one wheel to avoid a rollover.
It is still another object of the disclosed embodiments to provide a biasing force to at least one caster in response to a manual signal.
It is a further objective of the present invention to conserve air pressure with the use of a pneumatic reservoir.
Disclosed in embodiments herein is a zero turning radius vehicle, comprising the improvement of at least one caster supporting a portion of said vehicle weight, and being operatively biased in response to an accelerometer.
The disclosed embodiments relate to a slope sensitized pneumatic system capable of providing a counteracting bias to the caster wheels when traversing an incline, whereby air cylinders, connected to the caster axis, neutralize the gravitational forces.
The disclosed Slope Traversing System does not turn the front casters of the ZTR mower, but merely provides a balancing force to offset the turning force induced in the casters by gravity when the mower is traversing a slope. As a result, the system does not steer the mower and the operator cannot feel any operation differences between operating the mower on flat ground and operating the mower on a slope.
The aforementioned aspects and other objectives and advantages of the disclosed embodiments can be achieved as described in further detail below.